The present invention relates to volumetric pumping which can be used for paste-like materials, in particular unvulcanized rubber.
The methods of processing rubber products require, in various stages of their manufacture, a quantitative dosing of the unvulcanized rubber.
For example, at the time of the production of the mixes one generally proceeds by weighings. For the application of the rubber product onto a tire blank, Patent Application EP 0 264 600 proposes the use of a cylinder piston unit in order to permit volumetric dosing due to the precisely determined character of the volume swept over by the piston acting as an extrusion member. Unfortunately, the process is an intermittent one since, when the cylinder is empty, it is necessary to refill it before being able to effect a new dosing.
The use of screw extruders makes it possible to make passage from the raw material to the extruded products continuous. However, screw extruders are not volumetric, particularly during their starting and stopping phases. Screw extruders can extrude a determinable volume only in the case of perfectly established conditions: stabilized temperature and no variations in losses of head at the outlet from the extruder. Furthermore, in the case of screw extruders, when changing from one mix to another having different physical properties, for instance a different binder, the extruded output for a given speed of rotation of the screw will be different. One necessary condition in order for an extruder or a pump to be able to be considered volumetric is that the extruded output depend only on a control parameter of said extruder or pump (for instance, the speed of rotation of an input shaft) and does not depend significantly on the physical properties of the material to be extruded.